rman backup 对于truncate和drop等相关操作的extent到底是怎么处理的,这里通过rman backup 结合odu证明出来,在较新版本的rman中,rman backup 并未完全的备份这些被认为不需要的extent.
创建模拟环境

SQL> select * from v$version;
BANNER
----------------------------------------------------------------
Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - Prod
PL/SQL Release 10.2.0.4.0 - Production
CORE    10.2.0.4.0      Production
TNS for Linux: Version 10.2.0.4.0 - Production
NLSRTL Version 10.2.0.4.0 - Production
SQL> create tablespace xifenfei datafile '/u01/oracle/oradata/XFF/xifenfei01.dbf'
   2 size 10m autoextend on maxsize 10g;
Tablespace created.
SQL> conn chf/xifenfei
Connected.
SQL> create table t_xifenfei tablespace xifenfei
  2  as
  3  select * from dba_objects;
Table created.
SQL> insert into t_xifenfei
  2  select * from dba_objects;
50055 rows created.
SQL> commit;
Commit complete.
SQL> select BYTES from dba_free_space where TABLESPACE_NAME='XIFENFEI';
     BYTES
----------
    983040
SQL> select BYTES from v$datafile where name='/u01/oracle/oradata/XFF/xifenfei01.dbf';
     BYTES
----------
  12582912
SQL> select 12582912-983040 from dual;
12582912-983040
---------------
       11599872
SQL> select object_id,data_object_id from dba_objects where object_name='T_XIFENFEI';
 OBJECT_ID DATA_OBJECT_ID
---------- --------------
     51833          51833
--这里我们得到信息有:
--1.dataobj#=51833
--2.使用数据文件空间为:11599872

rman备份no truncate table 数据文件

[oracle@xifenfei ~]$ rman target /
Recovery Manager: Release 10.2.0.4.0 - Production on Thu Dec 15 06:00:05 2011
Copyright (c) 1982, 2007, Oracle.  All rights reserved.
connected to target database: XFF (DBID=3440302261)
RMAN> backup tablespace xifenfei format '/u01/oracle/oradata/tmp/no_truncate_xifenfei';
Starting backup at 15-DEC-11
using target database control file instead of recovery catalog
allocated channel: ORA_DISK_1
channel ORA_DISK_1: sid=158 devtype=DISK
channel ORA_DISK_1: starting full datafile backupset
channel ORA_DISK_1: specifying datafile(s) in backupset
input datafile fno=00005 name=/u01/oracle/oradata/XFF/xifenfei01.dbf
channel ORA_DISK_1: starting piece 1 at 15-DEC-11
channel ORA_DISK_1: finished piece 1 at 15-DEC-11
piece handle=/u01/oracle/oradata/tmp/no_truncate_xifenfei tag=TAG20111215T060343 comment=NONE
channel ORA_DISK_1: backup set complete, elapsed time: 00:00:03
Finished backup at 15-DEC-11

truncate table 操作

[oracle@xifenfei ~]$ sqlplus / as sysdba
SQL*Plus: Release 10.2.0.4.0 - Production on Thu Dec 15 06:03:58 2011
Copyright (c) 1982, 2007, Oracle.  All Rights Reserved.
Connected to:
Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options
SQL> truncate table chf.t_xifenfei;
Table truncated.

rman备份truncate table 数据文件

RMAN> backup tablespace xifenfei format '/u01/oracle/oradata/tmp/truncate_xifenfei';
Starting backup at 15-DEC-11
using target database control file instead of recovery catalog
allocated channel: ORA_DISK_1
channel ORA_DISK_1: sid=140 devtype=DISK
channel ORA_DISK_1: starting full datafile backupset
channel ORA_DISK_1: specifying datafile(s) in backupset
input datafile fno=00005 name=/u01/oracle/oradata/XFF/xifenfei01.dbf
channel ORA_DISK_1: starting piece 1 at 15-DEC-11
channel ORA_DISK_1: finished piece 1 at 15-DEC-11
piece handle=/u01/oracle/oradata/tmp/truncate_xifenfei tag=TAG20111215T060445 comment=NONE
channel ORA_DISK_1: backup set complete, elapsed time: 00:00:01
Finished backup at 15-DEC-11
[root@xifenfei ~]# ls -l /u01/oracle/oradata/tmp/*_xifenfei
-rw-r----- 1 oracle oinstall 11640832 Dec 15 06:03 /u01/oracle/oradata/tmp/no_truncate_xifenfei
-rw-r----- 1 oracle oinstall   630784 Dec 15 06:04 /u01/oracle/oradata/tmp/truncate_xifenfei

odu挖rman备份前数据文件

ODU> unload dict
CLUSTER C_USER# file_no: 1 block_no: 89
TABLE OBJ$ file_no: 1 block_no: 121
CLUSTER C_OBJ# file_no: 1 block_no: 25
CLUSTER C_OBJ# file_no: 1 block_no: 25
found IND$'s obj# 19
found IND$'s dataobj#:2,ts#:0,file#:1,block#:25,tab#:3
found TABPART$'s obj# 266
found TABPART$'s dataobj#:266,ts#:0,file#:1,block#:2121,tab#:0
found INDPART$'s obj# 271
found INDPART$'s dataobj#:271,ts#:0,file#:1,block#:2161,tab#:0
found TABSUBPART$'s obj# 278
found TABSUBPART$'s dataobj#:278,ts#:0,file#:1,block#:2217,tab#:0
found INDSUBPART$'s obj# 283
found INDSUBPART$'s dataobj#:283,ts#:0,file#:1,block#:2257,tab#:0
found IND$'s obj# 19
found IND$'s dataobj#:2,ts#:0,file#:1,block#:25,tab#:3
found LOB$'s obj# 151
found LOB$'s dataobj#:2,ts#:0,file#:1,block#:25,tab#:6
found LOBFRAG$'s obj# 299
found LOBFRAG$'s dataobj#:299,ts#:0,file#:1,block#:2393,tab#:0
ODU> scan extent tablespace 6
scan extent start: 2011-12-15 06:12:28
scanning extent...
scanning extent finished.
scan extent completed: 2011-12-15 06:12:28
ODU> unload table chf.t_xifenfei object 51833
Unloading table: T_XIFENFEI,object ID: 51833
Unloading segment,storage(Obj#=51833 DataObj#=51833 TS#=6 File#=5 Block#=11 Cluster=0)
100110 rows unloaded
--这里可以看到odu全部找到被truncate掉的记录条数

使用rman 备份后数据文件

SQL> shutdown immediate
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> exit
Disconnected from Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options
[oracle@xifenfei odu]$ rm /u01/oracle/oradata/XFF/xifenfei01.dbf
[oracle@xifenfei odu]$ rman target /
Recovery Manager: Release 10.2.0.4.0 - Production on Thu Dec 15 06:14:00 2011
Copyright (c) 1982, 2007, Oracle.  All rights reserved.
connected to target database (not started)
RMAN> startup mount;
Oracle instance started
database mounted
Total System Global Area     318767104 bytes
Fixed Size                     1267236 bytes
Variable Size                104860124 bytes
Database Buffers             205520896 bytes
Redo Buffers                   7118848 bytes
RMAN> restore datafile 5;
Starting restore at 15-DEC-11
using target database control file instead of recovery catalog
allocated channel: ORA_DISK_1
channel ORA_DISK_1: sid=157 devtype=DISK
channel ORA_DISK_1: starting datafile backupset restore
channel ORA_DISK_1: specifying datafile(s) to restore from backup set
restoring datafile 00005 to /u01/oracle/oradata/XFF/xifenfei01.dbf
channel ORA_DISK_1: reading from backup piece /u01/oracle/oradata/tmp/truncate_xifenfei
channel ORA_DISK_1: restored backup piece 1
piece handle=/u01/oracle/oradata/tmp/truncate_xifenfei tag=TAG20111215T060445
channel ORA_DISK_1: restore complete, elapsed time: 00:00:01
Finished restore at 15-DEC-11

odu挖rman还原后数据文件

ODU> scan extent tablespace 6
scan extent start: 2011-12-15 06:14:43
scanning extent...
scanning extent finished.
scan extent completed: 2011-12-15 06:14:43
ODU>  unload table chf.t_xifenfei object 51833
Unloading table: T_XIFENFEI,object ID: 51833
Unloading segment,storage(Obj#=51833 DataObj#=51833 TS#=6 File#=5 Block#=11 Cluster=0)
4774 rows unloaded
--odu只找到极少数数据4774/100110

通过odu挖rman备份前和备份后的数据文件,得知rman backup备份的过程,对绝大多数truncate的表的原始数据未正常备份(为什么是绝大多数,我无法给出解释),这里也可以看出rman backup并非是真正意义上的完全物理上复制(和rman copy还是有区别,copy不能完全被取代)